1. Field of the Invention
The present invention relates to an endoscope used in the medical field, and in particular to an endoscope, the insertion portion of which is made small in diameter.
2. Description of the Related Art
An endoscope is composed so that the insertion portion inserted into a body cavity is connected to the body control portion held by hands and operated by an operator, and a universal cord detachably connected to a light source unit and a processor is led out from the body control portion. The endoscope observation means consisting of an illumination portion and an observation portion is attached to the distal end of the insertion portion, by which inspections and diagnoses are carried out in a body cavity. In addition, a treatment equipment lead-out port for leading out forceps and treatment equipment are provided at a position adjacent to the endoscope observation means in order to apply a treatment to an affected part. An injection nozzle, etc., for a rinsing fluid to rinse an observation portion is further mounted at the distal end of the insertion portion.
Herein, an illumination portion to illuminate the inside of a body cavity is provided, as described above, in addition to the observation portion because the inside of a body cavity is dark. The illumination portion is composed by mounting an illumination lens to the distal end of the light guide led from the universal cord to the inside of the insertion portion via the body control portion. However, it is necessary to irradiate uniform illumination light to as a wide area as possible from the illumination portion. Therefore, the illumination portion is provided with at least two points and is disposed at both sides between which the observation portion is placed. The observation portion is provided with an object optical system including an object lens and a solid-state image pickup device. The solid-state image pickup device is incorporated on a substrate to which a predetermined number of wires are connected. Accordingly, since the solid-state image pickup device has a large size, it will occupy a wide space if it is disposed in the direction orthogonal to the axial line of the insertion portion. Therefore, the solid-state image pickup device and the substrate thereof are disposed so as to be oriented in the axial direction of the insertion portion. And, a prism is provided, which bends the optical axis of the object lens oriented in the axial direction of the insertion portion by 90°.
Forceps, radio frequency treatment equipment, or appropriate treatment equipment in compliance with a purpose and use is inserted into the treatment equipment lead-out port, and treatment such as extraction of an affected part is carried out. A treatment equipment insertion channel that becomes a path of the treatment equipment is connected to the treatment equipment lead-out port. The treatment equipment insertion channel is led to the body operation portion and reaches the treatment equipment lead-in portion secured at the body control portion.
Therefore, in order to improve efficiency and function of treatment by the endoscope observation means, the inner diameter of the treatment equipment insertion channel and the pore diameter of the treatment equipment lead-out port are made as large as possible, and it is necessary to lead out large-sized treatment equipment. On the other hand, since the insertion portion of the endoscope is inserted into a body cavity of a patient and it is necessary to pass the insertion portion through a narrow portion in the insertion channel, it is favorable that the outer diameter dimension of the insertion portion is made as small as possible in order to relieve the burden of a patient and to improve the insertion efficiency. Therefore, such an endoscope is proposed by JP-B-5-6456, which is composed so that, by setting the object optical system and solid-state image pickup device so as to take a predetermined positional relationship with respect to the treatment equipment insertion channel, thinning in the diameter of the insertion portion is attempted, and simultaneously the treatment equipment insertion channel is made large.
According to JP-B-5-6456, the endoscope is composed so that the optical axis of the object optical system, secured at the distal end composition of the insertion portion, which composes the observation system is bent roughly orthogonally, and an image is formed on a solid-state image pickup device, a plane passing through the center axis of the object optical system and parallel to the solid-state image pickup device is positioned in the vicinity of the center axis of the treatment equipment insertion channel. In summary, the optical axis of the object optical system is bent by 90° by using a prism and an image is formed on the solid-state image pickup device. Therefore, with respect to the widest solid-state image pickup device among the respective members disposed at the distal end of the insertion portion, the treatment equipment insertion channel being the next largest member is offset equivalently to the distance between the solid-state image pickup device and the center position of the object optical system, wherein it is possible to effectively utilize the space at the distal end of the insertion portion, and possible to make large the inner diameter of the treatment equipment insertion channel.
Although, in the composition of JP-B-5-6456, great importance is attached to the positional relationship between the observation portion consisting of the object optical system and the solid-state image pickup device and the treatment equipment insertion channel, the members incorporated in the endoscope are not limited thereto, wherein many other components are provided. In particular, arrangement of the illumination portion that composes the endoscope observation means greatly influences, along with the observation, the quality of images showing the inside of a body cavity, which is obtained by the observation portion. Idealistically, it is necessary that illumination light is uniformly irradiated without unevenness onto the entirety of the field of vision of the observation portion For this reason, it is composed that at least two illumination portions are provided, and these two illumination portions are disposed at both sides between which the observation portion is placed, and the line connecting both the centers of both the illumination portions passes through the center of the observation portion or is positioned in the vicinity thereof, and it is necessary that the distances from both the illumination portions to the observation portion are made as equal as possible.
However, the endoscope disclosed in JP-B-5-6456 is composed so that the observation portion and the treatment equipment insertion channel are disposed at a predetermined position at the distal end of the insertion portion, and the illumination portion is disposed in an excess space. Therefore, the line connecting the illumination portions provided with two points is greatly deviated from the center of the observation portion, and the differences between both the illumination portions and the observation portions are great. In JP-B-5-6456, a difference is brought about for the calibrations of both the illumination portions, by which unevenness in illumination is attempted to be reduced. However, unevenness in illumination still occurs. As a result, the quality of an image obtained by the endoscope observation means is lowered, wherein there remains a problem in that the accuracy in inspections and diagnoses is lowered.